Unlike the majority of United States jurisdictions, grand jury witnesses in New York automatically receive transactional immunity, unless they decide to waive immunity, in writing, before the grand jury, and with their lawyer present. A witness who receives transactional immunity can never be prosecuted for any crime involved in their testimony before the grand jury. Even witnesses who actually confess to crimes before a grand jury can never be prosecuted for those crimes.
Prosecutors must be careful in deciding what witnesses to call before a grand jury, so that they do not immunize a witness for a crime, and must, when appropriate, demand that a witness waive transactional immunity.